Dual mode undercarriage for tracked vehicle

ABSTRACT

A vehicle with a frame connecting a driver wheel, an idler wheel and mid-roller wheels, an endless track belt being tensioned around the driver wheel and the idler wheel and being in contact with the mid-roller wheels on a lower run thereof, the mid-roller wheels being arranged in boogies, including a front boogie having a first pivot axis, a middle boogie and a rear boogie arranged in tandem having a second pivot axis, wherein the first pivot axis and said second pivot axis act as load transfer pivots.

FIELD OF THE INVENTION

The present invention relates to tracked vehicles. More specifically,the present invention is concerned with a dual mode undercarriage fortracked vehicles.

BACKGROUND OF THE INVENTION

A range of tracked vehicles, such as working vehicles, including asphaltpavers, crawlers, combine harvesters, earthmoving machines andtransporters for example, experience shifts of their center of gravityor instabilities in balance, due to their carrying varying loads as theyare used to spread material for example or to their supporting mobileheavy implements, or to high speed.

Indeed, it may happen that an additional weight due to materialtransported or unloaded or to an implement such as a screed on a paverfor example, or a higher speed, destabilizes the vehicles, resulting inpoor performance of the vehicles, premature failure of the tractionsystem thereof, and damage to the underlying ground.

There is still a need for a dual mode undercarriage for trackedvehicles.

SUMMARY OF THE INVENTION

More specifically, in accordance with the present invention, there isprovided a vehicle with a frame connecting a driver wheel, an idlerwheel and mid-roller wheels, an endless track belt being tensionedaround said driver wheel and said idler wheel and being in contact withsaid mid-roller wheels on a lower run thereof, the mid-roller wheelsbeing arranged in boogies, including a front boogie, a middle boogie anda rear boogie, the front boogie having a first pivot axis, and themiddle and rear boogies forming a tandem having a second pivot axis,wherein the first pivot axis and the second pivot axis act as loadtransfer pivots.

Other objects, advantages and features of the present invention willbecome more apparent upon reading of the following non-restrictivedescription of specific embodiments thereof, given by way of exampleonly with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1 is a schematic view of a tracked vehicle according to anembodiment of an aspect of the present invention;

FIG. 2 is a view of a lateral belt arrangement of the vehicle of FIG. 1;

FIG. 3 illustrates the position of the axis of a rear tandem in the beltarrangement of FIG. 2, relative to the center of gravity of the vehicle;

FIG. 4 is a detailed view of the rear part of the lateral beltarrangement of FIG. 2;

FIG. 5 illustrates a behavior of the front part of the lateral beltarrangement of FIG. 2;

FIG. 6 show stoppers in an alternative of the belt arrangement of FIG.2;

FIG. 7 illustrates a behavior of the rear part of the lateral beltarrangement of FIG. 2;

FIG. 8 illustrates the lateral belt arrangement of FIG. 2 in a firstmode; and

FIG. 9 illustrates the lateral belt arrangement of FIG. 2 in a secondmode.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is illustrated in further details by the followingnon-limiting examples.

As shown schematically in FIG. 1, a belt laying vehicle 100 comprises atrack belt arrangement on each lateral side thereof, each track beltarrangement comprising an endless belt 12 entrained about an idler wheel14 and a driver wheel 16 mounted in supporting relation to a frame 10,and mid-rollers 18. The frame 10 provides a flexible connection for theundercarriage including the wheels, the axles of the wheels, and thetrack belt 12. An implement 110, such as a screed for example, in thecase of a paver, is located at one extremity of the vehicle, forexample.

The vehicle is a tracked vehicle, such as a working vehicle, includingfor example asphalt pavers, crawlers, combine harvesters, earthmovingmachines and transporters for example, which experiences shifts of itscenter of gravity or instabilities in balance, due to load distributionor speed for example.

As shown in details in FIG. 2, the endless track belt 12 is tensionedaround the driver wheel 16, the idler wheel 14 and is in contact withthe mid-roller wheels 18 on a lower run thereof. A tensioning system(not shown) allows controlling the tension of the belt 12, as well knownin the art.

The mid-roller wheels 18 are here arranged as boogies including a frontboogie 20 of axis 22, and rear boogies 24 and 26 assembled in a tandem28 of pivot axis 30.

The center of gravity of the vehicle may be determined without load (seelabel CG_(empty) in FIG. 3), which corresponds to a maneuver mode, ortravel mode, of the vehicle, and then with load thereon (see labelCG_(loaded) in FIG. 3), which corresponds to a working mode of thevehicle.

In the case of an asphalt paver for example, CG_(empty) corresponds tothe center of gravity of the paver when the hopper is empty and thescreed is up; while CG_(loaded) corresponds to the center of gravity ofthe paver when the hopper is loaded and the screed is on the float.

The frame 10 is tiltable around the pivot axis 30 of the rear tandem 28,located between these centers of gravity of the unloaded and loadedvehicle, whereby a varying length of the belt 12 is pressed down intocontact with the underlying ground 36. The positioning of the pivot axis30 is a function of characteristics of the vehicle, such as for examplecharacteristics of the screed in the case of a paver as discussedhereinabove, and may take into account security factors.

The adjustment further comprises providing stoppers 32 and 34 about theframe 10, as best seen in FIG. 4.

An up stopper 32 consists, for example, of a calibrated plate, welded tothe frame 10, to which a part of the tandem 28 comes in abutment,thereby stopping the pivot movement of the tandem 28 around the axis 30.The position of the plate 32 is determined so as to allow a target rangeof forward tilt of the tandem 28 before abutment with the plate 32. Infact, the position of the plate 32 determines an angle at which the loadon the vehicle is transferred on the undercarriage, and the extent ofthis transfer.

A down stopper may consist of a member 34, also welded to the frame 10for example, which comes into abutment with a finger 39 of the tandem28, thereby limiting the rearward tilt. This stopper 34 limits the tiltrearwards and protects the drive wheel 16 from impacts with theunderlying ground.

The stoppers 32 and 34 are pre-adjusted, when assembling the vehicle,according to the characteristics of the belt, such as the hardness ofthe rubber for example, or the diameter of the drive wheel 16, tocontrol the rotation of the axis 30 so as to use only a desired front orrear part of the belt 12. The part of the belt 12, which is not requiredfor a current operation, is made to slightly lift off the ground 36under action of the stoppers.

As the center of gravity of the vehicle passes over the pivot axis 30 ofthe tandem 28 to the front, the vehicle tilts towards the front, untilthe plate 32 stops movement of the tandem 28 about the pivot axis 30. Atthis point, the tandem 28 is fixed, and the vehicle may only pivot aboutthe boogie 24. As the load increases, the center of gravity of thevehicle keeps shifting forwards and eventually reaches the level of theaxis 22 of the front boogie 20.

As shown in FIG. 5, the axis 22 of the front boogie 20 supports andstabilizes the load in the working mode of the vehicle. The axis 22,located between the boogie 24 and the idler wheel 14, generally acts tolimit the load on the idler wheel 14, by limiting the unbalance towardsthe front of the vehicle.

The axis 22 acts as a load transfer pivot until the center of gravity ofthe vehicle crosses the pivot axis 22 from the rear, as will now bedescribed.

As the load increases and the boogie 20 sinks down into the track 12,the idler wheel 14 comes into contact with the underground surface,thereby limitating the sinking of the boogie 20 in the track by anupwards reaction (see arrow (A) in FIG. 5). Once the idler wheel 14 isin contact with the underground surface, any additional load isdistributed between all mid rollers, with the axis 22 of the boogie 20acting as a load transfer pivot (FIG. 5—arrows (B) and (C)).

Alternatively, in the case of a rigid belt 12′ such as a metal belt or amixed metal and composite belt, as a substitute for the sinking of theboogie 20 into the resilient belt 12, it may be contemplated using amember, in rubber or in a deformable material, either added to theboogie 20 (see member 40 in FIGS. 6 a and 6 b), or included in theboogie 20 (see material 42 in FIG. 6 c), which deforms under load. Inthis case, sinking of the instead of the boogie 20 is obtained bydeformation of this member.

As best seen in FIG. 7, in the working mode, the vehicle is tiltedtowards the front. As it does, the undercarriage structure, includingthe drive wheel 16, follows the movement, except for the tandem 28,which is stopped by the stopper 34. The drive wheel 16 is lifted up fromthe plane of the ground surface 36, thereby lying on a plane 33different from the plane of the mid rollers 18 c, 18 d, 18 e and 18 f.The mid rollers 18 c and 18 d are in equilibrium under the load, and themid roller 18 e becomes a stabilizator as the pressure from the belt 12back on the mid roller 18 f acts as a tensioner, a cord being createdbetween the drive wheel 16, which is lifted up, and the boogies 24 and26, which remain on the ground.

Such actions and reactions interplay maintains the stability of thevehicle during accelerations, the rear tandem 28 allowing tensioning thetrack 12 during operations on the front part of the vehicle, i.e. on therear end thereof as the drive wheel 16 is lifted from the ground 36, therearest boogie 26 being in contact with the underground 36 with only oneof the two mid-rollers thereof, the other one of the two mid-rollersthereof floating (see mid roller 18 f in FIG. 9) and acting fortensioning the track 12 in case of oscillation of the vehicle due tomovement of the vehicle. The occasional load on the wheel 18 f on theground 36, which tends to act on it upwards (see FIG. 7), acts on thefloating wheel 18 f downwards, which tensions the belt 12 since thedrive wheel 16 is off the ground, as described hereinabove.

Thus, the position of the tandem 28 is defined and adjusted to yieldoptimized load transfer performances, by controlling the position ofsupporting points and pivoting points depending of the load distributionon the vehicle, the vehicle operating from the maneuverability mode tothe working mode as the center of gravity of the vehicle is shifted.

In FIG. 8, the center of gravity CG of the vehicle being located at therear of the axis 30, the front idler wheel 14, the mid-rollers 18 a, 18b and the rear drive wheel 16 are off the underlying ground 36, whereasthe mid-rollers 18 c, 18 d, 18 e and 18 f are on the ground 36,maintained by stopper 34.

In FIG. 9, the center of gravity CG of the vehicle being located infront of the axis 30, the front idler wheel 14, as well as the reardrive wheel 16 and the rear mid-roller 18 f are off the ground 36, whilethe mid-rollers 18 a, 18 b, 18 c, 18 d and 18 e are on the ground 36,maintained by stopper 32.

Hence, according to the displacement of the center of gravity of thevehicle, different modes are allowed, which correspond to differentconformation of the wheels and belt, as will now be described.

In the maneuverability mode, a short working surface of the endless belt12 is achieved, as shown in FIG. 8, with only mid-rollers 18 c, 18 d, 18e and 18 f on the ground 36.

In the working mode, the working surface of the endless belt 12 isincreased, as shown in FIG. 9, with mid-rollers 18 a, 18 b, 18 c, 18 dand 18 e on the ground 36.

As people in the art will appreciate, the present system may be appliedto utility tracked vehicles submitted to load shifts or unbalances, fora dynamic load and balance control.

For example, asphalt pavers, when they have a loaded hopper and screedon the float, i.e. before and during paving, typically benefit from theworking mode described hereinabove, and, when the hopper is empty andthe screed up once the paving operation is over, typically benefit fromthe mobility mode described hereinabove.

The present system and method provide increased stability, which resultsin increased traction quality and speed, and allows reducing mechanicalwear and stress by optimized weight distribution and adaptable steeringcharacteristics. People in the art will appreciate that the presentinvention therefore allows increasing the productivity of the vehiclesand of activities making use of them.

The present undercarriage allows a dynamic control of load distribution,thereby optimizing performance and reliability of the vehicle, andconstancy in traction characteristics while maintaining agility,stability and directional control of the vehicle.

Although the present invention has been described hereinabove by way ofspecific embodiments thereof, it can be modified, without departing fromthe nature and teachings of the subject invention as defined in theappended claims.

1. A vehicle with a frame connecting a driver wheel, an idler wheel andmid-roller wheels, an endless track belt being tensioned around saiddriver wheel and said idler wheel and being in contact with saidmid-roller wheels on a lower run thereof, said mid-roller wheels beingarranged in boogies, including a front boogie, a middle boogie and arear boogie, said front boogie having a first pivot axis, and saidmiddle and rear boogies forming a tandem having a second pivot axis,wherein said first pivot axis and said second pivot axis act are loadtransfer pivots.
 2. The vehicle of claim 1, wherein said frame istiltable around said second pivot axis, whereby a varying length of saidbelt is pressed down into contact with the underlying ground.
 3. Thevehicle of claim 1, wherein said frame comprises a first stopperlimiting a pivot movement of said tandem about said second pivot axis tothe front, and a second stopper limiting a pivot movement of said tandemabout said second pivot axis to the rear.
 4. The vehicle of claim 3,wherein said first stopper is a plate, a part of said tandem coming inabutment with said plate at a first angle of forward rotation of saidtandem about said second pivot axis.
 5. The vehicle of claim 3, whereinsaid second stopper is a member, which comes into abutment with saidtandem plate at a second angle of rearward rotation of said tandem aboutsaid second pivot axis.
 6. The vehicle of claim 3, wherein said firststopper stops a front movement of said tandem about said second pivotaxis, as the center of gravity of the vehicle passes over said secondpivot axis to the front.
 7. The vehicle of claim 3, wherein said firstpivot axis transfers the load from the front to the rear until thecenter of gravity of the vehicle crosses said first pivot axis to therear.
 8. The vehicle of claim 3, wherein, at an unbalance limit wheresaid front boogie sinks relative to said belt, resulting in said idlerwheel to come into contact with the underlying ground, said first pivotaxis transfers the load from the front to the rear.
 9. The vehicle ofclaim 8, wherein said belt is in a resilient material, said front boogiesinking into said belt at said unbalance limit.
 10. The vehicle of claim8, wherein said belt is one of: i) rigid and ii) semi-rigid, said frontboogie comprising a member, said member deforming at said limit load;said front boogie sinking relative to said belt when said member deformsunder said limit load.
 11. The vehicle of claim 1, wherein said firstpivot axis acts as a transfer pivot to the rear until the center ofgravity of the vehicle crosses said first pivot axis to the rear; and asthe center of gravity of the vehicle passes over the second pivot axisfrom the rear, a first stopper prevents further tilt towards the rear,whereas as the center of gravity of the vehicle passes over the secondpivot axis to the front, a second stopper prevents further tilt towardsthe front.
 12. The vehicle of claim 11, wherein said stoppers arepre-adjusted to control a rotation of the second pivot axis, to use onlya desired part of the belt, a remaining part of the belt being made toslightly lift off the ground under action of the respective stopper. 13.The vehicle of claim 11, said endless track belt being made in aresilient material, wherein said first pivot axis acts to limit a loadon the idler wheel until a unbalance limit, said front boogie sinkinginto the belt and the idler wheel coming into contact with theunderground surface at said unbalance limit; said first pivot axis, oncethe idler wheel is in contact with the underground surface, transferringany additional load to the rear of the vehicle.
 14. The vehicle of claim11, said endless track belt being made in one a rigid or mixed material,wherein said front boogie comprises a deformable member, said firstpivot axis acting to limit a load on the idler wheel until an unbalancelimit, said deformable member being deformed and causing a sinking ofsaid front boogie and the idler wheel to come into in contact with theunderground surface at said unbalance limit; said first pivot axis thentransferring any additional load to the rear of the vehicle.
 15. Thevehicle of claim 11, wherein said endless track belt is made in aresilient material.